The problem of punctures, namely the problem of how to enable a vehicle to continue its travel despite a substantial or complete loss of pressure of one or more of its tyres or how to avoid a loss of air following a perforation, dates back from the very start of the use of wheels fitted with inflated tyres.
One solution very often proposed is to add a self-sealing layer to the inner wall of the tyre.
To be usable, such a self-sealing layer must meet many conditions of a physical and chemical nature. In particular, it must be effective over a very wide range of operating temperatures, throughout the lifetime of the tyres. It must be capable of sealing off perforations or holes when the responsible perforating object, which we will call a “nail”, remains in place. After the nail has been removed, the self-sealing layer must be able to fill up the hole. It is preferable for the material of the self-sealing layer not to pass completely through the wall of the tyre so as to form a protrusion or “plug” on the outside. These plugs are effective for avoiding leaks, but if for any reason they are cut off, the leak may no longer be sealed off.
Document U.S. Pat. No. 4,426,468 presents self-sealing layers for tyres, based on a crosslinked high-molecular-weight butyl rubber, the formulation of which is adjusted so as to meet given values of the stress at break, elongation at break and crosslinking density characteristics and thus, in particular, to prevent the material of the self-sealing layer from passing through the wall of the tyre into the hole left after the nail has been removed.
Document EP 1 090 069 B1 discloses a self-sealing composition with 100 parts by weight of a styrene-based thermoplastic elastomer, 110 to 190 parts by weight of an adhesive, 80 to 140 parts by weight of a liquid plasticizer and 2 to 20 parts by weight of an additive. That document provides no information regarding the physical characteristics of the compositions.